Gas tube control



April 17, 1951 H H. WITTENBERG Gxs TUBE CONTROL Filed Nov. a. 1949 Hl/X/L/H/PY 6,45 WL m55 @Mw/7 M45/IV INVENTOR ATTORNEY Patented Apr. 17, 1951 GAS TUBE CONTROL Hubert H. Wittenberg, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application November 8, 1949,'Seral No. 126,062

(Cl. S15-237)` 9 Claims. 1

This invention relates to gas tube circuits.

It is a frequently recurring problem in gas tube operation to =provide extinction of the gas tube supplying power to a load. Various means have been devised to secure extinction of the tube, particularly tubes having control grids, so that the grid will again take control of the time of initiation of current conduction.

It is an object of the present invention to pro-u vide a particularly emcient means of extinction of a gas tube.

It is another object of the invention to provide a simple means for extinguishing a gas tube.

A further object of the invention is to provide means for extinguishing a gas tube which means Will be simple in operation and readily timed with respect to the initiation pulse so that adjustable periods of conduction of the gas tube are readily obtained.

Another object of the invention is to provide a gas tube circuit especially well adapted for motor control circuits. Y

In accordance with the invention I provide a delay network or pulse forming line from which pulses of deiinite duration and substantially of square waveshape are applied across at least a portion of the anode-to-cathode impedance or f the gas tube by discharging the delay line through an auxiliary gas tube and thro-ugh the impedance.

The foregoing and other objects, advantages,

and novel features of the invention will become more apparent from the following description in which:

Fig. l is a circuit diagram schematically illustrating Vone embodiment of the invention in which a delay line is discharged through an auxiliary gas tube and'through a portion of the anode circuit impedance of the main gas tube, which includes a D.C. motor armature winding, to obtain an extinction pulse;

Y Fig. 1A is an exemplifying graph vof the voltage across the impedance of Fig. l; and

Fig. 2 is a circuit diagram schematically illus trating another embodiment of the invention in which the delay line is discharged through an auxiliary gas tube and a cathode impedance in the cathode circuit of the main gas tube.

Referring now more particularly to Fig. 1, a load which may include impedances Iii and I2 in the anode-to-cathode circuit of a gas' tube I4 is supplied by a D.C. supply source I6 serially connected between the cathode I8 and anode 2t of the main gas tube I4. The main gas tube I4 has a control element 22 to initiate conduction ,in the tube when suitable voltages are applied to vmay be the armature of a D.C. motor.

2 the various electrodes. The load I ll, for example, It will be further understood that the term gas tube" is intended to include thyratrons, ignitrons, or the like, that is, both the type of tube utilizing a liquid cathode and the type utilizing asolid cathode. Control element 22 is connected to an initiation pulse circuit 24. A delay line 25 which may be composed of a plurality of series inductors 23 and shunt capacitors 30 to simulate a transmission line, having terminals 32 and 34 for connection at the one end and open circuited at the end remote therefrom.

Such delay lines are well known, for example, as described in U. S. Patent No. 2,470,550 to John Evans, granted on May 17, 1949.

An auxiliary gas tube 36 has its cathode 38 connected to delay line terminal 3G and itsV anode 40 connected to one terminal of impedance I0, here illustrated as the armature winding or a D.C. motor, the other terminal of impedance Il) being connected to the delay line terminal 32. The delay line 3!) may be charged through a high impedance inductor 42 preferably at the open circuited end, the said inductor being also connected to a voltage supply 44. The control element 45 of gas tube 3S is connected to a second pulse circuit 4&3. Both the initiation pulse circuit 24 and the second pulse circuit 48 are connected to a source of alternating current 5I) which times the occurrence of the pulses in the circuits. However, the source 5I) might be of random pulses. The second pulse circuit 48 is also provided with means 52 for phase shifting or timingthe occurrence of the pulse which it produces with respect to those of the initiation pulse circuit.

In operation, the source 50 may be a sine wave vgenerator of low frequency and the initiation pulse circuit 24 may produce, once for each cycle oi the sine wave and in a denite phase relationship therewith,y an initiation pulse 22 of short.

y duration, for example ten microseconds, which .setting of the phasingA means 52;

pulse is applied to control element 46 of auxiliary gas tube 36, whereupon the delay line 26 discharges through auxiliary gas tube 36 and the matching termination I0, it being understood that the impedance I substantially matches the characteristic impedance of the line 26. A substantially square wave of voltage will now be produced across impedance I0 in a polarity tending to make the anode 20 of the main gas tube I4 negative with respect to the cathode I8 thereof. The time duration of the substantially square wave of Voltage depends upon the constants of the line 26 and is designed to exceed the extinction time of the main gas tube I4. I have used a delay line providing a pulse having a time Width of about 500 microseconds. The amplitude of the extinction pulse of voltage also depends upon the voltage supplied by source 44, Which again may be a rectied source of current deriving its energy from the source U. The amplitude and duration of the pulse are chosen to be conservatively suicient to extinguish the gas tube I4 and allow the grid 22 thereof to regain control of the initiation of conduction therein. After the termination of the pulse, due to high impedance of inductor 42 at the pulse recurrence rate, there is insucient voltage to maintain conduction in the auxiliary gas tube 36 which therefore ceases conduction and the control element 46 thereof regains the control of the initiation of conduction in the auxiliary gas tube 36.

I have found that the circuit is especially well adapted for the control of a D.C. mo-tor, the speed of which, or the output of which, is to be closely controlled. In such a case the initiation pulse circuit, as a single example, may comprise a vacuum tube clipper circuit such as are well known, to convert the sinusoidal voltage variations from source 56 to substantially square wave voltages. The square wave voltage may then be differentiated, as by a resistor-capacitor combination, to provide one positive going (and one negative going) pulses each cycle. These pulses are fed to control element 22, the positive-going pulses initiating conduction in tube I4. The second pulse circuit may be similar, except to include a phasing control 52 before the conversion of the sinusoidal-to-square wave voltage circuit. Such phasing control may include a goniometer type phase shifter with two stator windings to which the source voltage is applied in 90 phase relationship, to provide a eld rotating at the frequency of the source, and a rotor Winding, the phase of the voltage induced therein with respect to the source frequency being then substantially linearly dependent on its angular' position in the rotating eld. The output from the rotor, which may be set by control 52, is then applied to the square Wave circuit and then to a diierentiator. When more energy is to be supplied armature IU, the control 52 is set to cause the pulses from circuit 48 applied to control element 45 to lag farther behind the pulses applied to grid 22 than when less energy is to be supplied armature I6. Then the time of conduction through tube I4 is increased. Notwithstanding, smooth motor operation results, with an ordinary 60 cycle per second supply, because the inertia of the motor and its load is ample to smooth out the eiect of the two pulses per cycle applied to the armature. The motor may be run for periods of say one or two minutes, or more, at speeds controlled by the phasing control 52. It will be understood that other pulsing circuits might be 4 used for other purposes, particularly where other loads are used.

Starting or stopping al1 power to the load may be accomplished, for example, by a switch 'I3 arranged to sequentially disconnect source 50 from circuit 48. Tube I4 is extinguished after the disconnection of circuit 24, and the later disconnection of source 50 from pulse circuit 48 causes tube 36 to cease conduction by the self-extinction feature of the circuit as heretofore explained, if it is not in a non-conducting point in the cycle. It will be noted that no rheostat control is required, which is advantageous since large rheostats require constant servicing and attention and are not capable of the close regulation of power secured by a proper phasing control 52.

If the source 50 is of random pulses, for each of which it is required to develop considerable energy to operate a relay or the like, by passing a high current through tube I4, the pulsing circuits might comprise well known one-pulse multivibrator arrangements. The phasing control 52 might be such as to alter the length of a multivibrator pulse, and the derived initiation and conduction pulses, which may be positive going pulses .derived by differentiation of the multivibrator pulses, once for every random pulse of source 50, then produces an appreciable controlled time of flow of current in tube I4, which may pass through a relay winding or the like as load.

If a simple resistor-capacitor network had been used in place of the delay line 26, the energy which necessarily would have to pass through auxiliary gas tube 36 to secure extinction of main gas tube I4 would be greater. This will be apparent by considering, as shown in Fig. 1A, a negative pulse having a sharp leading edge 60 and a logarithmically rising trailing edge 62 as would result from use of such a network. By the means of the invention, the auxiliary gas tube provides a substantially square wave pulse having a sharp leading edge 64 and a sharp trailing edge 66. If the extinction voltage to be applied at the point 68 of Fig. l, the junction between impedances I 0 and I2, is assumed to be represented by the line l0, it will be clear from the iigure that the energy in the pulses is indicated by the area between the pulse and the line 12, which is the normal Voltage at the point 68 before the extinction pulse is applied. From Fig. 1A it is very apparent that the curve having the sharp leading edge 66 and the logarithmically rising trailing edge 62 encloses more area and indicates dissipation of more energy than the substantially square wave enclosed by the leading edge 64 and the trailing edge 66. Moreover, the recovery time is minimized so that the main gas tube I4 may again be placed in operation with an initiation pulse at the earliest possible time after it has been extinguished. Accordingly, I am able to use a smaller auxiliary gas tube 36 in order to extinguish the main gas tube I4 than would be possible with a mere resistor-capacitor network. Again, were a mere resistor-capacitor circuit to be used, with some combinations, the logarithmically decaying pulse approaches the D.C. voltage supplied from source 44 and tube 36 may go into continuous conduction. My arrangement avoids such difficulties. Moreover, by suitably undermatching the line 30, the anode voltage of tube 36 can be made to swing somewhat negatively at the termination of the substantially square wave pulse, .doubly insuring extinction of tube 36.

Referring now more particularly to Fig. 2, the

D main gas tube I4 has a cathode impedance 68, which may be part of the load if desired. As before, an initiation pulse circuit 24 is connected to the grid 22 of main gas tube I4. Auxiliary gas tube 36 is connected in circuit with delay line 26. The extinction pulse circuit 48, is connected to the control element 46 of the auxiliary tube 36. Both the initiation and extinction pulse circuits 24 and 48 are connected to a source of alternating potential 59. Delay line 26 is charged through an inductor 'I I`by a D.C. voltage supply 14. Since i the delay line and auxiliary gas tube circuit arrangement are connected in this case to a cathode resistor 69, the polarity of the pulse must be such as to make the cathode I8 more positive and tend to make it positive with respect to the voltage of anode 20 of main gas tube I4 in order to extinguish the gas tube I4.

The operation of this circuit will be clear to those skilled in the art from what has been stated -r in connection with Fig. 1. After the main gas lll delay line, and means to apply a pulse of short duration to said auxiliary gas tube control element, said delay line being connected in shunt across at least a portion of said impedance with the characteristic impedance of said delay line substantially matching said impedance portion and said auxiliary gas tube being connected serially with said delay line, said delay line connection being in the sense to provide an extinction voltage pulse across said portion of said impedance upon discharge of said line through said auxiliary gas tube, whereby application of said short duration pulse causes application of a substantially square wave voltage extinction pulse across said impedance portion to extinguish current ow in said main gas tube.

3. In the circuit claimed in claim 2 wherein said main gas tube has a control element, the

' combination further comprising an initiation tube I4 is conducting, an extinction pulse applied larly eiiicient and desirable means for extinguishing a gas tube and as especially well adapted to the control of a D.C. motor. It will be obvious that many variations can be made in the specic arrangements shown. For example, the control of the motor speed may be accomplished by varying the frequency of the source 59, leaving xed the time of extinction of the controlled main tube with respect to initiation of conduction therein, but varying the frequency of the conduction periods of the controlled tube. Many forms of delay line, using either lumped or distributed reactances are known which might be used for delay line 30.

Having thus described the invention, what I claim is:

l. In a circuit for extinguishing current flow in a main gas tube having an anode-to-cathode circuit including an impedance, the combination comprising a delay line, an auxiliary gas tube, and means to charge said delay line, said delay line being connected in shunt across at least a portion of said impedance with the characteristic impedance of said delay line substantially matching said impedance portion and said auxiliary gas tube being connected serially with said delay line, said delay line connection being in the sense to provide an extinction voltage pulse across said portion of said impedance upon discharge of said fine through said auxiliary gas tube, whereby a substantially square Wave voltage extinction pulse is applied across said impedance portion to extinguish current flow in said main gas tube.

2. In a circuit for extinguishing current flow in a main gas tube having an anode-tO-cathode circuit including an impedance, the combination comprising a delay line, an auxiliary gas tube having a control element, means to charge said Al l) pulse circuit connected to said main gas tube control element to initiate conduction therein, said short duration pulse circuit being interconnected with said initiation pulse circuit to apply said short duration pulse to said auxiliary gas tube element at a predetermined adjustable time after initiation of current flow in said main gas tube.

4. In the circuit claimed in claim 1, said means to charge said delay line comprising a high impedance inductor and a voltage supply.

5. In the circuit claimed in claim 1, the combination comprising a D.C. motor having a winding, said impedance including said Winding.

6. In the circuit claimed in claim l, said impedance portion being a portion of a useful load in the anode circuit of said gas tube.

7. In the circuit claimed in claim 1, said impedance portion being at least a portion of a cathode impedance of said main gas tube.

8. The method of extinguishing current flow in a main gas tube having an anode-to-cathode circuit including an impedance and comprising a delay line and an auxiliary gas tube serially connected therewith, said method comprising the steps of charging said delay line, and thereafter discharging said delay line through said gas tube across said impedance in a substantially square wave pulse to extinguish current ow in said main gas tube.

9. The method claimed in claim 8 further comprising the steps of rst initiating conduction in said rnain gas tube, and thereafter discharging the charged delay line through said auxiliary gas tube.

HUBERT H' WITTENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,691,395 kLangmuir NOV. 13, 1928 2,053,016 Wilder Sept. 1, 1936 2,372,106 Nagel Mar. 20, 1945 2,416,327 Labin Feb. 25, 1947 2,490,562 Van Dorsten Dec. 6, 1949 

